Who exactly will do this? No major car company would risk their reputation selling a car with that programmed into its software.
What's the risk, exactly?
Our car has an "ultra-economy mode" where the motor turns off when stationary - many cars already have this.
Our car can park itself - many cars already have this.
Our car will find a parking space, optimizing the route to and from the parking garage - that seems logical, why would a company not do that?
Our company will optimize the route to and from the parking garage, and the time spent in the garage vs on the road based on price vs economy of the car - why would a company not do that?
The problems only occurs when hundreds of cars independently make their own decision to drive as slowly as possible to and from the parking space.
(Edit: someone else pointed out that UPS routes their trucks to avoid left turns. This isn't too dissimilar to that - they do it to improve fuel economy, this would be done to improve costs too)
Even if groups of hackers installed this on their cars, I can't imagine this movement gaining enough critical mass to honestly be a concern.